Carbon-fiber-reinforced plastics (CFRPs), which comprise carbon fibers and matrix resins, have excellent strength, stiffness, or other characteristics and are used for various applications, for example, primary structure members of flying machines, automotive members, windmill blades, and chassis for various electronic machines. For such applications, particularly important physical properties mainly include physical strength, for example, impact strength, elastic modulus, flexural strength, and interlaminar toughness.
In order to improve such physical properties, it is being devised to add a variety of fillers to a CFRP containing a matrix resin (for example, an epoxy resin component) and a carbon fiber.
A typical example of the fillers includes an inorganic compound particle as represented by a silica. Such a filler itself has a high elastic modulus and is suitable for improving the elastic modulus or flexural strength of the CFRP. However, the filler does not necessarily have a good interfacial affinity with the matrix resin, thus decreasing the impact strength, the interlaminar toughness, or other physical properties.
As a method for improving the impact strength, addition of a rubber-like soft material is also known. Unfortunately, such a soft material reduces the elastic modulus or the flexural strength in contrast to the silica or other inorganic compounds.
Meanwhile, addition of a thermoplastic resin powder as an intermediate material between the inorganic compound and the rubber-like soft material is also being developed.
For example, Japanese Patent Application Laid-Open Publication No. 2012-211310 (JP-2012-211310A, Patent Document 1) discloses a carbon-fiber-reinforced composite comprising a resin layer and a carbon fiber layer on either main side of the resin layer, wherein the resin layer comprises a matrix resin, a resin particle containing a specific alicyclic polyamide resin, and an electroconductive particle having an average particle diameter larger than the resin particle, the carbon fiber layer contains a carbon fiber, and there is a 12-μm or less difference between the average thickness of the resin layer and the average particle diameter of the resin particle.
For the composite described in this document, the difference between the average thickness of the resin layer and the average particle diameter of the resin particle is reduced to 12 μm or less to prevent the interlaminar toughness from decreasing due to variation in the thickness of the resin layer. In order to reduce the difference, it is inevitably necessary to increase the proportion of the resin particle in the resin layer. For example, this document discloses that the proportion of the resin particle in the resin layer is preferably 20 to 70% by volume. In each of working examples, the resin particle is used at a ratio of 15 parts by weight relative to 155 parts by weight of a thermosetting resin composition.
Unfortunately, such a large proportion of the resin particle easily reduces the physical properties of the composite. Moreover, such a large proportion increases a viscosity (thixotropy) of a mixture containing the matrix resin and the resin particle, and thus the mixture is hard to be compounded with the carbon fiber. In some cases, the compounding itself is difficult.